(Reuters) - An unmanned minehunting vehicle developed by Lockheed Martin Corp has shown improved reliability in new tests, moving it a step closer to use on U.S. warships, Navy officials said on Thursday.

An improved version of the Remote Minehunting System has completed 850 hours of testing, paving the way for 10 weeks of development and operational testing this fall, which should allow the system to go into use in 2015.

"Ultimately, this system is going to take sailors out of the minefield," Steve Lose, the Navy's program manager for the Lockheed system, told Reuters in a telephone interview.

Hunting for mines in harsh, murky waters is a critical mission for the Navy. It is keen to shift that work to unmanned systems and keep sailors out of harm's way. Sea mines are inexpensive weapons that are readily available to terrorists, rogue nations and potential adversaries.

Lockheed's Remote Minehunting System combines a diesel-powered, stealthy unmanned vehicle, or Remote Multi-Mission Vehicle (RMMV), with advanced sonar sensors to help Navy ships search for mines faster and more efficiently.

The RMMV sends real-time visual images back to the ship and allows them to be collected for future analysis.

Lose said the testing completed last week showed the equipment operated successfully, on average, for 115 hours before breaking down, up from 45 hours previously and far exceeding the Navy's 75-hour requirement.

The system is a key part of the mine countermeasures package planned for the Navy's new Littoral Combat Ships, relatively small vessels used close to shore. Early technical and reliability issues prompted the Navy to require improvements. Delays in fielding that system, and a separate anti-submarine warfare package, have sparked concerns in Congress, which is keeping a close watch on the LCS program.

Lockheed and Australia's Austal are building two different models of the new warships, which are designed to help patrol coastal areas, find mines and chase down potential attackers.

The Navy decided three years ago to halve its planned order of RMMVs to 54, which raised the cost of each of the remaining vehicles and triggered a review. The reliability improvements were imposed as a condition for allowing the $1.4 billion program to continue.

Completion of the extensive at-sea testing of the system, coupled with a recent contract for its integration onto the new LCS warships, is good news for Lockheed, which is also one of two companies building the new warships.

If the next phase of testing goes well, Lockheed stands to receive orders for 44 more RMMVs in coming years, Lose said.

Lockheed said it would work closely with the Navy to get the new equipment on board the ships as quickly as possible.

"With the completion of the reliability testing, we are a big step closer to addressing the need for a safe, efficient mine warfare capability for the U.S. Navy," Steve Froelich, program director at Lockheed's mission systems unit, told Reuters in an emailed statement.